Calcium tolerant deflocculant for drilling fluids

ABSTRACT

A high calcium containing drilling fluid having a 0.1-10 pounds per barrel of a deflocculant which is a water-soluble acrylic polymer which contains from 5-50 mole percent of one or more of the following: 
     Sulfoethyl acrylamide; or 
     Acrylamide and Sulfoethyl acrylamide; or 
     Ethyl acrylate and Sulfoethyl acrylamide; or 
     Acrylamide and Sulfophenyl acrylamide; or 
     Acrylamide and Sulfomethyl acrylamide.

INTRODUCTION

The invention relates to a method of preventing the flocculation ofdrilling fluids which contain high amounts of calcium.

In the drilling of oil wells and other deep weels by rotary drillingprocesses, it is now the practice to recirculate an aqueous fluid called"drilling mud" down through the hollow drill pipe, acrossthe face of thedrill bit, and upward through the drill hole. The drilling mud serves tocool and lubricate the drill bit, to raise the drilling cuttings to thesurface of the ground, and to seal the sides of the well to prevent lossof water and drilling fluids into the formation through which the drillhole is being bored. After each passage through the well, the mud ispassed through a settling tank or trough wherein the sand and drillcuttings are separated, with or without screening. The fluid is thenagain pumped into the drill pipe by a mud pump.

In the formulation of drilling fluids, it is common to add a materialknown as a deflocculant. These deflocculants are usually materialscapable of neutralizing positive edge charges of clay particles.Interparticle attractions due to positive edge charges are considered tobe the cause of the flocculation of the active components of the fluid.

Common deflocculants used to treat drilling fluids are low molecularweight polyacrylic acids. These polymers are good as deflocculants whenthe amount of calcium in the drilling flid is relatively low. When theamount of calcium exceeds 100 ppm, polyacrylic acid or otherdeflocculants such as sodium acid pyrophosphate (SAPP) are not toosuccessful in preventing flocculation.

The invention, therefore, is directed to a method of preventing theflocculation of drilling fluids which contain high amounts of calcium,e.g. greater than 100 ppm.

THE INVENTION

The invention comprises an improved high calcium containing drillingfluid which contains a major portion of drilling fluid and adeflocculating amount of a water-soluble copolymer or terpolymer ofacrylic acid which contains from 5-50 mole percent of:

Sulfoethyl acrylamide; or

Acrylamide and Sulfoethyl acrylamide; or

Ethyl acrylate and Sulfoethyl acrylamide; or

Acrylamide and Sulfophenyl acrylamide; or

Acrylamide and Sulfomethyl acrylamide, or a mixture thereof.

In a preferred embodiment of the invention, the copolymer or terpolymerof acrylic acid contains from 5-20 mole percent of one of the above.

Generally, 0.1-2 pounds of polymer per barrel of drilling fluid issufficient to prevent flocculation of the additives in the drillingfluid, although 0.1-10 pounds per barrel may be needed. The amount ofpolymer needed is generally related to the solids content of thedrilling fluid, so that increases in the solids content of the drillingfluid generally increase the polymer requirements. The dosage may alsobe regulated so as to provide between 0.1--up to about 2 ppm of polymerper each part of calcium present in the fluid.

The molecular weight of the polymers can vary between as little as 1000up to as much as 50,000. A preferred molecular weight range is about4,000 to 20,000.

The polymers of the invention are useful in preventing flocculation of avariety of drilling fluids. These include:

(1) lime muds;

(2) gypsum muds of "gyp muds";

(3) sea water muds;

(4) fresh water muds contaminated with cement or other sources ofsoluble calcium.

The following table lists polymers actually used by sample number,composition, percent actives and weight average molecular weight:

    ______________________________________                                        SAM-                         %**                                              PLE                          AC-                                              NO.   POLYMER COMPOSITION    TIVES   MW*                                      ______________________________________                                        1     Acrylic Acid/Acrylamide/                                                                             31.9     4,530                                         Sulfoethylacrylamide                                                    2     Acrylic Acid/Acrylamide/                                                                             31.9    10,600                                         Sulfoethylacrylamide                                                    3     Acrylic Acid/Acrylamide/                                                                             31.9    15,700                                         Sulfoethylacrylamide                                                    4     Acrylic Acid/Acrylamide/                                                                             35.8    25,000                                         Sulfomethylacrylamide                                                   5     Acrylic Acid/Acrylamide/                                                                             30.3     4,500                                         Sulfomethylacrylamide                                                   6     Acrylic Acid/Acrylamide/                                                                             35.8    18,900                                         Sulfomethylacrylamide                                                   7     Acrylic acid/Sulfoethyl acrylamide                                                                   17.8    30,900                                   8     Acrylic acid/Acrylamide/Sulfoethyl                                                                   30.8    14,000                                         Acrylamide                                                              9     Acrylic acid/Ethyl acrylate/                                                                         26.4     3,680                                         Sulfoethyl acrylamide                                                   10    Acrylic acid/Acrylamide/Sulfophenyl                                                                  24.3    11,500                                         Acrylamide                                                              11    Acrylic acid/Acrylamide/Sulfomethyl                                                                  24.2    16,400                                         Acrylamide                                                              12    Acrylic acid/Acrylamide/Sulfomethyl                                                                  35.5    10,300                                         Acrylamide                                                              13    Acrylic acid/Acrylamide/Sulfomethyl                                                                  26.7     2,900                                         Acrylamide                                                              ______________________________________                                         *Weight average molecular weight determined via GPC using polystyrene         sulfonate standard.                                                           **% Actives as the acid                                                  

EXAMPLE 1

To illustrate the invention, the following is presented by way ofexample:

A representative mud system was used for testing these polymers. Thecomposition of the base fluid of Example I was as follows:

300 pounds per barrel (ppb) tap water

20 ppb bentonite clay

30 ppb Kaolinite

276 ppb barite (weighting agent)

pH 10 with sodium hydroxide

1.25 ppb gypsum

The compositions of all the examples were prepared in a standard 350milliliter laboratory barrel. The examples provided were actuallyperformed on a laboratory scale. All compositions specified arepresented on the basis of a real barrel (42 gallons). The calculationswere made assuming 1 gram per milliliter of water, 1 ppb=1 gram per 350milliliter in a laboratory barrel.

Initial Rheology--Before Aging

The base fluids of each of the examples was dosed with sample polymer toprovide the number of pounds of sample per barrel of drilling fluidindicated in the Tables. With no aging, the following results wereobtained with the base fluid of Example I:

    ______________________________________                                                       Conc             10 Sec.                                                                             10 Min.                                 Sample No.     (lb/bbl) YP      Gel-  Gel                                     ______________________________________                                        11             .25      18      16    20                                      (Acrylic acid/Acrylamide/                                                     Sulfomethyl Acrylamide)                                                       11             .5       16      15    35                                      (Acryllc acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       13             .25      22      18    22                                      (Acrylic acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       13             .5       18      12    40                                      (Acrylic acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       12             .25      18      13    40                                      (Acrylic acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       12             .5       11       5    16                                      (Acrylic acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       ______________________________________                                         *YP = Yield Point. An effective deflocculant reduces the numerical value      of the YP. Yield point, 10 second gel and 10 minute gel tests were            determined according to the American Petroleum Institute document, API RP     13B, Section 2.                                                          

EXAMPLE 2

The composition of the base fluid of Example 1 was aged at 250° F. forsixteen hours. The following results were obtained:

    ______________________________________                                                       Conc             10 Sec.                                                                             10 Min.                                 Sample No.     (lb/bbl) YP      Gel   Gel                                     ______________________________________                                        11             .25      15      24    45                                      (Acrylic acid/Acrylamide/                                                     Sulfomethyl Acrylamide)                                                       11             .5       13      18    60                                      (Acrylic acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       13             .25      18      22    60                                      Acrylic acid/Acrylamide                                                       Sulfomethyl Acrylamide                                                        13             .5       18      16    65                                      (Acrylic acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       12             .25      14      20    70                                      (Acrylic acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       12             .5        9       4    30                                      (Acrylic acid/Acrylamide                                                      Sulfomethyl Acrylamide)                                                       ______________________________________                                         *YP = Yield Point. An effective deflocculant reduces the numerical value      of the YP. Yield point, 10 second gel and 10 minute gel tests were            determined according to the American Petroleum Institute document, API RP     13B, Section 2.                                                          

EXAMPLE 3

The following mud system was used for testing these polymers. Thecomposition of the base fluid was as follows:

299 pounds per barrel (ppb) tap water

20 ppb bentonite clay

30 ppb Kaolinite

276 ppb barite (weighting agent)

pH 10 with sodium hydroxide

1.25 ppb gysum

After aging at 250° F. for 16 hours, the following results wereobtained:

    ______________________________________                                                                Conc    10 Sec.                                                                             10 Min.                                 Sample No.       YP     lb/bbl  Gel   Gel                                     ______________________________________                                        7                27     0.2     13    56                                      (Acrylic acid/Sulfoethyl                                                      acrylamide)                                                                   8                21     0.2     14    42                                      (Acrylic acid/acrylamide/                                                     Sulfoethyl acrylamide)                                                        9                21     0.2     13    41                                      (Acrylic acid/Ethyl acrylate/                                                 Sulfoethyl acrylamide)                                                        10               25     0.2     14    45                                      (Acrylic acid/Acrylamide/                                                     Sulfophenyl acrylamide)                                                       ______________________________________                                         *YP = Yield Point. An effective deflocculant reduces the numerical value      of the YP. Yield point, 10 second gel and 10 minute gel tests were            determined according to the American Petroleum Institute document, API RP     13B, Section 2.                                                          

EXAMPLE 4

In this example, the composition of the base fluid was as follows:

299 pounds per barrel (ppb) tap water

20 ppb bentonite clay

30 ppb Kaolinite

276 ppb barite (weighting agent)

pH 10 with sodium hydroxide

1.5 ppb gypsum

Without aging, the following results were obtained:

Initial Rheology--No Aging

    ______________________________________                                                        Conc            10 Sec.                                                                             10 Min.                                 Sample No.      (lb/bbl) YP     Gel   Gel                                     ______________________________________                                        Blank                    76     60    80                                      1               0.5      28     33    76                                      (Acrylic Acid/Acrylamide                                                      Sulfoethylacrylamide)                                                         2               0.5      22     27    100                                     (Acrylic Acid/Acrylamide/                                                     Sulfoethylacrylamide)                                                         3               0.5      22     22    93                                      (Acrylic Acid/Acrylamide                                                      Sulfoethylacrylamide)                                                         4               0.5      24     25    86                                      (Acrylic Acid/Acrylamide/                                                     Sulfomethylacrylamide)                                                        5               0.5      36     40    53                                      Acrylic Acid/Acrylamide/                                                      Sulfomethylacrylamide)                                                        6               0.5      16     15    70                                      (Acrylic Acid/Acrylamide/                                                     Sulfomethylacrylamide)                                                        ______________________________________                                         *YP = Yield Point. An effective deflocculant reduces the numerical value      of the YP. Yield point, 10 second gel and 10 minute gel tests were            determined according to the American Petroleum Institute document, API RP     13B, Section 2.                                                          

Aged at 150° F. Overnight

    ______________________________________                                                        Conc            10 Sec.                                                                             10 Min.                                 Sample No.      (lb/bbl) YP     Gel   Gel                                     ______________________________________                                        Blank                    265    172   220                                     1               0.5      79     68     96                                     (Acrylic Acid/Acrylamide                                                      Sulfoethylacrylamide)                                                         2               0.5      61     58    110                                     (Acrylic Acid/Acrylamide/                                                     Sulfoethylacrylamide)                                                         3               0.5      36     50    100                                     (Acrylic Acid/Acrylamide/                                                     Sulfoethylacrylamide)                                                         4               0.5      59     63    132                                     (Acrylic Acid/Acrylamide/                                                     Sulfomethylacrylamide)                                                        5               0.5      135    125   205                                     (Acrylic Acid/Acrylamide/                                                     Sulfomethylacrylamide                                                         6               0.5      42     45     70                                     (Acrylic Acid/Acrylamide/                                                     Sulfomethylacrylamide)                                                        ______________________________________                                         *YP = Yield Point. An effective deflocculant reduces the numerical value      of the YP. Yield point, 10 second gel and 10 minute gel tests were            determined according to the American Petroleum Institute document, API RP     13B, Section 2.                                                          

We claim:
 1. An improved high calcium containing aqueous drilling fluidcontaining clay particles and from 0.1-10 pounds per barrel of anacrylic acid/acrylamide/sulfophenyl acrylamide deflocculant terpolymerwhich has a molecular weight within the range of from 1,000 to 50,000,wherein the acrylamide and sulfophenyl acrylamide components are presentin a total amount of 5-50 mole percent.
 2. The drilling fluid of claim 1wherein the terpolymer has a molecular weight within the range of 4,000to 20,000.